June 11, 1644: The Barometer Gets Its First Practical Airing

Image: Science Photo Library/Wikimedia

1644: Italian physicist Evangelista Torricelli demonstrates the principles of the mercury barometer, an instrument he invented the previous year.

In 1641, Torricelli was working as an assistant to Galileo, then quite old and near death, performing vacuum experiments with mercury, when he noticed that the height of the liquid in a vacuum tube varied from day to day based on changes in atmospheric pressure.

Remaining in Florence after Galileo’s death, Torricelli continued with his mentor’s work while developing what would become a very valuable scientific instrument.

The barometer is used for measuring atmospheric pressure, which is especially helpful in weather forecasting. A falling barometer heralds an approaching storm, while a rise in air pressure generally means fair weather.

The principles established by Torricelli have changed little over the centuries and today’s modern barometers closely resemble those produced in the 17th century.